Recently, a transmission device that supports an optical transport network (OTN) is provided as a transmission device transmitting information. Such a transmission device changes a client-side clock frequency to an OTN-side clock frequency because the client-side clock and the OTN-side clock have different frequencies and transmits client data that is a transmission target.
Upon receiving a client signal from a client that is a data transmission source, the transmission device stores the client data included in the received client signal in a first-in-first-out (FIFO). In addition, the transmission device reads the client data from the FIFO at the OTN-side clock frequency. Then, the transmission device maps the client data read from the FIFO and stuff data that reduces a phase difference between the OTN-side clock and the client-side clock onto the payload of an optical channel transport unit (OTU) frame.
The transmission device generates a Cm value and a Cnd value and stores the Cm value and the Cnd value in the header of the OTU frame. The Cm value indicates an amount of the client data mapped onto the payload, and the Cnd value is a value resulting from adding fluctuation in data for a certain period of time. Then, the transmission device transmits the OTU frame to a counterpart transmission device through the OTN.
The counterpart transmission device, meanwhile, extracts the client data from the received OTU frame and stores the extracted client data in the FIFO. In addition, the counterpart transmission device extracts the Cm value and the Cnd value from the received OTU frame and calculates a Cn value that is the difference value between the Cm value and the amount of logical data in the OTU frame, based on the extracted Cm value and the Cnd value. Then, the counterpart transmission device regenerates the OTN-side clock from the OTU frame and generates the clock that is used by the client being the transmission source of the client data, by using the regenerated OTN-side clock, the extracted Cm value, and the Cn value.
More specifically, the counterpart transmission device compares a frequency resulting from adding the proportion of the client data to the payload of the OTU frame to the frequency of the regenerated OTN-side clock with the frequency of the clock generated as the client-side clock. Then, the counterpart transmission device controls the frequency of the generated clock to reduce the frequency gap resulting from the comparison, reads the client data from the FIFO based on the generated clock, and transmits the read client data to the client that is a transmission destination.
Japanese Laid-open Patent Publication No. 2007-150423 is an example of the related art.